1. Field of the Invention
The invention relates to light source driving devices, and particularly to a light source driving device used in liquid crystal display (LCD) backlight module.
2. Description of Related Art
Conventionally, discharge lamps, especially Cold Cathode Fluorescent Light sources (CCFLs) are often used as light sources in LCD panels. Typically, the light sources need high voltages to operate. Recently, LCD panels have become larger and larger, and as a result, the number of light sources needed in the LCD panels has increased.
FIG. 3 is a conventional light source driving device. The driving device is used for driving a light source module 32 comprising a plurality of light sources, which comprises a driving switch circuit 30, a transformer circuit 31, a feedback circuit 33 and a Pulse Width Modulation (PWM) controller 34. The driving switch circuit 30 converts a received direct current (DC) signal to an alternating current (AC) signal. The transformer circuit 31 converts the AC signal to a sine-wave signal to drive the light source module 32. The feedback circuit is connected between the transformer circuit 31 and the PWM controller 34, for feeding current flowing through the light source module 32 back to the PWM controller 34. The PWM controller 34 controls the AC signal output from the driving switch circuit 30 according to the current flowing through the feedback circuit 33. Thus, the current from the light source module 32 can be controlled.
In the above conventional discharge lamp driving device, the feedback signal from the transformer circuit 31 not only includes lamp current, but leakage current as well, which comes from stray capacitances between the light sources and ground. Obviously, the leakage current affects the accuracy of the feedback signal.